Contained within the boundaries of the Amazon are over a million different species of animals ranging from jaguars to monkeys to  tarantulas.  There are over 500, 000 species of insects and spiders alone.  The diversity of animals in the Amazon is unlike that of any part of the world.  It is estimated that hundreds of thousands of species in the Amazon have not as of yet been scientifically classified.

As mentioned earlier, the vast majority of the animals are insects and spiders.  This is due to natural selection.  When insects and spiders first evolved in the Amazon, they were few in numbers but as time went by, insects and spiders entered different habitats within the Amazon and adapted to that environment.   Soon, insect and spider species were so different that they could not interbreed (A species is defined as a group of organisms that can reproduce with fertile offspring.).   This is called adaptive radiation.  Alfred Wallace, British scientist, noticed this on his trip to the Amazon.  From this he would develop the theory of natural selection.  Charles Darwin developed the same theory but published it earlier.  Many other animals have undergone adaptive radiation in the Amazon and the list include birds, wild cats, and primates.

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